1. Field of the Invention
The present invention relates to an electrostatically attracting electrode and a method of manufacture thereof. More particularly, this invention relates to an electrostatically attracting electrode suited for holding a substrate on a sample table by using an electrostatic force when a semiconductor substrate such as a wafer is subjected to plasma process or heat treatment, and a method of manufacturing such an electrode.
2. Description of the Prior Art
Conventional electrostatically attracting electrodes used in substrate processing equipment have been primarily of a so-called monopole electrode type, in which a high negative voltage is applied to the electrode that attracts the substrate and a circuit that is grounded from the substrate to the ground through a plasma is provided. One example is an electrostatic chuck disclosed in Japanese Patent Laid-Open No. 216224/1994. The monopole electrode has features such as a simplified electrostatic attraction circuit and a constant, applied electrostatic potential at the substrate. The disadvantage of the monopole electrode is that the electrostatic charge cannot be removed unless a plasma is generated.
In the electrostatic chuck described in Japanese Patent Laid-Open No. 216224/1994, a ceramic that forms an electrostatic attraction member is brazed at low temperatures to an electrode block. The electrostatic attraction ceramic must be finished to a predetermined small thickness because too thick an attraction ceramic cannot produce an attraction force. The electrostatic chuck is formed by sticking the thick ceramic plate to the electrode block and polishing it to a predetermined thickness.
Another example of the electrostatically attracting electrode using the monopole electrode is an electrostatic chuck described in Japanese Patent Laid-Open No. 275708/1994. This electrostatic chuck is fabricated by bonding, through an insulating film, an electrostatic attraction film to the surface of a susceptor (block) mace of a metal such as aluminum. By this method the electrostatic attraction film is formed by using such materials as SiC having a particular range of resistivity and forms a portion corresponding to the wafer attraction surface in one piece.
Another example similar to the above is an electrostatic chuck used in a plasma process equipment described in Japanese Patent Laid-Open No. 260449/1994.
The electrode of a so-called dipole type has a positive and a negative electrode arranged in the plane of a substrate surface to be held by attraction and has an advantage that the electrostatic attraction charge can be eliminated regardless of the presence or absence of a plasma. Examples of the electrostatically attracting electrode using the dipole electrode include a wafer chuck described in U.S. Pat. No. 5,055,964. This electrostatic chuck described in this reference is a type of chuck which has a second electrode within a first electrode. The first electrode can be made from a single, conducting block. Similarly, the second electrode is made from a single, conducting block. After joining the first electrode and the second electrode, the top surface of assembled chuck is machined. The top surface of the assembled chuck is machined to final dimension, smoothness, and flatness. Finally, a layer of insulator is applied to the top clamping surface of chuck. Such application may be any suitable method, including anodization.
As the wafer increases in size (from 6 inch to 8 inch, further from 8 inch to 12 inch), the difference in thermal expansion between the electrostatic attraction film and the electrode block a problem may occur depending on the electrode temperature, and hence the manufacture of large electrostatic attraction films becomes difficult. For example, there is a problem that it is difficult to handle a ceramic board described in Japanese Patent Laid-Open No. 216224/1994 during a bonding step unless the ceramic board is thick enough to some extent, in other words, the board has a sufficient strength.
In the case in which the electrostatic attraction film is formed by flame spraying, there will be less of the above problems. The flame sprayed film, however, has problems that the breakdown voltage is low compared with that of the sintered material and that the physical property values required for electrostatic attraction such as the permittivity and the electric resistance are more difficult to control than their corresponding values of the sintered material.
Furthermore, because the electrostatic attraction film must not change in thickness and must be kept thin even when the wafer becomes large, its handling is very difficult. When the wafer is further increased in size, it will become even more difficult to make the electrostatic attraction film using a sintered material. That is, the sintered member as an electrostatic attracting layer has a smaller thickness compared with the size of the sintered member. It is difficult to handle the thin sintered member since it is easily cracked because of a small thermal strain.
It is a primary object of the present invention to provide an electrostatically attracting electrode and a method of manufacture thereof that can solve the above problems and can handle a large-size wafer. This object can be achieved by separating the electrode into a first electrode and a second electrode, providing a recess in a part of the first electrode, forming an insulating film in the recess, inserting and fixing a second electrode in the recess, planarizing the surfaces of the both electrodes, forming an electrostatic attraction insulating film over the electrodes, and then polishing the film to a predetermined thickness.
A second object of this invention is to provide an electrostatically attracting electrode and a method of manufacture of the electrostatically attracting electrode, which can be manufactured to a desired size with good precision to handle a large-size wafer and whose insulating film over the electrodes can be controlled easily. This object can be achieved by dividing an electrostatically attracting sintered material of the electrostatic attraction member, into a plurality of pieces and arranging them on the electrode block, bonding or mechanically fixing the electrostatic attraction member on the electrode block, flame-spraying an insulating film over the electrode block to which the electrostatic attraction member is fixedly attached, and polishing the surface of the electrode block covered with the insulating film to expose the surface of the electrostatic attraction member.